that was not working,
but i put this code, and it seems to be ok :
.menu-item-mega-parent .avia-menu-fx {
top: 115px !important;
}
.header-scrolled .menu-item-mega-parent .avia-menu-fx {
top: 72px !important;
}

the only things, that’s not ok is the z-index (the avia-menu-fx seems to be behind the layer-slider)